The fact is that, even from much closer by, it would be very difficult, if not impossible, to see the colors and contrasts. It is a matter of the sensitivity of our cone cells in the retina. Of course, when we are closer, we would receive more intensity of the light coming from the nebula, but spread over a much larger surface, what would again decrease the amount of light received by one specific cell. We easily see colors of objects that have “compact” (distributed on a small size) colors. That’s what our retina has been designed for and not for the immensely large objects like these ones. Anyhow, technology comes to our help… and allows us to reproduce the real colors…